Hip arthroplasty can be used to restore function to an injured or diseased hip joint. When performing surgical procedures such as hip arthroplasty, physicians generally attempt to damage as little tissue as possible to minimize trauma to the patient, reducing the time and effort required for the patient's recovery. To facilitate this goal, advances in medical technology have enabled minimally invasive surgical procedures, wherein a minimally necessary number of incisions are made and the incisions are as small as functionally possible. Accordingly, in minimally invasive procedures, the openings through which physicians perform procedures are relatively small, resulting in a limited range of motion and maneuverability for procedural tools and equipment. Thus, minimally invasive procedures provide benefits, such as minimizing trauma to the patient and reducing the patient's recovery, as well as challenges, such as reducing the workspace and range of motion for physicians and their tools during procedures.
For the purposes of surgical procedures, such as hip arthroplasty, positions and directions relative to the hip joint may be described using anatomical directions. Accordingly, as used herein, proximal refers to the direction toward to the hip joint, distal refers to the direction away from the hip joint, anterior refers to the direction toward to the front of the body, posterior refers to the direction toward to the back of the body, medial refers to the direction toward to the centerline of the body and lateral refers to the direction away from the centerline of the body. Additionally, aspects of the hip joint can be described relative to the anatomical planes: the transverse plane, which divides the body into a superior portion (nearer to the head) and an inferior portion (nearer to the feet); the sagittal plane, which divides the body into a left portion and a right portion; and the coronal plane, which divides the body into the anterior portion and the posterior portion.
In a total hip arthroplasty, both the “ball” and the “socket” of the hip joint are replaced with prosthetic device implants to form a new joint. The ball of the hip joint is often replaced by removing the femoral head from the proximal end of the femur, inserting a femoral prosthesis partially into the intramedullary canal of the femur, and coupling a ball to the proximal end of the femoral prosthesis. The socket of the hip joint is often replaced by removing bone from the acetabulum to create a cup-shaped opening and inserting an acetabular cup prosthesis into the cup-shaped opening. In a partial hip arthroplasty, either the ball or the socket of the hip joint may be replaced with a prosthetic device. If, after a total or partial hip arthroplasty, a subsequent medical event arises involving one of the hip implant prostheses, a procedure may be required to extract or remove the implanted prosthetic device to enable replacement with another prosthesis.
Inserting and extracting a femoral prosthetic device from a patient's femur generally require specific tools which engage with the femoral prosthetic device and enable a physician to apply sufficient force to the femoral prosthetic device. Because a tight fit between the femoral prosthetic device and existing femoral bone is desired, both insertion and extraction of a femoral prosthetic device generally requires application of a significant impact force to the femoral prosthetic device. Such an impact force is usually applied to an impact surface on the tool. The impact force is transferred through the tool to the femoral prosthetic device.
Due to the anatomy of the hip joint and the reduced range of maneuverability in minimally invasive hip arthroplasties, the tools for insertion and extraction are generally curved, like that in FIG. 1, to accommodate available access angles and to avoid unwanted contact with and impingement of bones and tissues during the procedures. The curved shapes of the tools, while providing some benefits, in turn present additional challenges and difficulties during insertion and removal of femoral prosthetic devices.
As shown in FIG. 1, for example, because the tool 10 is curved, the impact force FI applied to the impact surface 12 by the physician is offset from the transfer location 14 where the force is applied to the femoral prosthetic device through the tool 10. One problem that arises as a result of this offset 16 is the generation of a moment M about the transfer location 14. In other words, application of the impact force FI at the impact surface 12 generates a tendency for the tool 10 to rotate about the transfer location 14. Accordingly, to prevent the tool 10 from rotating about the transfer location 14 and maintain stability of the tool 10 during the procedure, the physician must apply a manual force FM to the tool 10 to oppose the moment M generated by the impact force FI.
By way of example, if the offset 16 between the axis of the impact force FI and the transfer location 14 is 50 mm and the physician grips the tool 10 at a gripping offset 22 that is 230.7 mm from the transfer location 14, the moment M generated at the transfer location 14 has a magnitude that is approximately ⅕ the magnitude of the impact force FI. Accordingly, to oppose the moment M, the physician must apply a manual force FM that is approximately ⅕ the magnitude of the impact force FI. If the impact force FI is, for example, 500 lbf, a physician has to apply a manual force FM that is approximately 100 lbf while also maintaining proper positioning of the instruments.
Another problem that arises due to the generated moment M is that the tip 18 of the tool 10 which engages the femoral prosthetic device at the transfer location 14 can be sheared off, becoming lodged in the femoral prosthetic device. As noted above, to counteract the moment M generated by the impact force FI applied to the tool 10, physicians must apply a sufficient opposing manual force FM. Instead of applying the manual force FM to oppose the moment M, however, some physicians have intuitively attempted to eliminate the moment M by hitting the edge of the impact surface 12, thereby applying the impact force FI at an angle 20 relative to the impact surface 12. By applying the impact force FI to the tool 10 at an angle 20, however, the physician generates a significant shear stress FS on the tip 18 of the tool 10 which engages the femoral prosthetic device. The shear stress FS has resulted in shearing off the tip 18 of the tool 10, requiring additional corrective measures to be undertaken during the procedure.
Given the above discussion, it would be advantageous to provide an improved femoral prosthesis including features enabling insertion/extraction with greater efficiency and less risk for error. It would also be advantageous to provide an improved insertion/extraction tool including features enabling insertion/extraction with greater efficiency and less risk for error. It would also be advantageous to provide an improved method for inserting/extracting femoral prosthetic devices with greater efficiency and less risk for error.